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Re: [Xen-devel] losetup -d fails when domU is destroyed

To: Kirk Allan <kallan@xxxxxxxxxx>
Subject: Re: [Xen-devel] losetup -d fails when domU is destroyed
From: Ewan Mellor <ewan@xxxxxxxxxxxxx>
Date: Mon, 8 May 2006 16:50:30 +0100
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On Mon, May 08, 2006 at 09:24:26AM -0600, Kirk Allan wrote:

> I do not see this happen very often, but every once in a while after a domU
> is destroyed the loop device is still in use.  From the /var/log/messages
> file I see:
> May 8 08:54:00 kdell logger: /etc/xen/scripts/block: remove
> XENBUS_PATH=backend/vbd/3/768
> In the xen-hotplug.log there is an entry
> ioctl: LOOP_CLR_FD: Device or resource busy
> It appears that when the /etc/xen/scripts/block script goes to remove the
> device with the losetup -d ?$node? that the device is still busy and the
> command fails.  But by the time you can enter losetup -d /dev/<loopdevice>
> from the command line, the device is no longer busy and the command
> succeeds.
> As a test I modified the /etc/xen/scripts/block script to sleep 1 and try
> the losetup -d again if the first try failed.  After many attempts to cause
> the problem, it finally happened.  The first losetup -d failed and the
> second succeeded.  Although this worked, it doesn't seem to be the correct
> solution to the underlying problem.  Any help or guidance would greatly be
> appreciated.

IIRC, we've had people report this before, but no-one's managed to get to the
root cause.  I'd be happy to take a patch that just sleeps and retries a few
times if you can't find the root cause yourself.

You might also speak with Kurt Garloff about bug #374
(http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=374) which is similar,
though in his case the losetup -d failed when the domain had crashed.


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